Multiple speed transmission

ABSTRACT

A family of transmission gearing arrangements produces nine forward and one reverse speed ratio by selective engagement of various combinations of three clutches or brakes. Each transmission gearing arrangement includes a front shiftable gearing arrangement configured to establish a variety of speed ratios between an intermediate shaft and an input shaft. These speed ratios include a reverse speed ratio, a zero speed ratio, two underdrive ratios, and a direct ratio. Each transmission also includes a rear shiftable gearing arrangement configured to selectively establish particular speed relationships. Engagement of a clutch in the rear shiftable gearing arrangement establishes an underdrive ratio between the output shaft and the intermediate shaft. Engagement of another clutch in the rear shiftable gearing arrangement constrains the speed of the input shaft to be a weighted average between the speed of the intermediate shaft and the output shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 13/569,467 filed Aug. 8, 2012, now U.S. Pat. No. 9,695,913, issued Jul. 4, 2017, the disclosure of which is hereby incorporated in its entirety by reference herein.

TECHNICAL FIELD

This disclosure relates to the field of automatic transmissions for motor vehicles. More particularly, the disclosure pertains to an arrangement of gears, clutches, and the interconnections among them in a power transmission.

BACKGROUND

Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Some types of engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. When the vehicle is at low speed, the transmission is usually operated at a high speed ratio such that it multiplies the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel efficient cruising. Typically, a transmission has a housing mounted to the vehicle structure, an input shaft driven by an engine crankshaft, and an output shaft driving the vehicle wheels, often via a differential assembly which permits the left and right wheel to rotate at slightly different speeds as the vehicle turns.

SUMMARY OF THE DISCLOSURE

A family of transmission gearing arrangements is disclosed. Each transmission gearing arrangement includes a front shiftable gearing arrangement configured to establish a variety of speed ratios between an intermediate shaft and an input shaft, including a reverse speed ratio, a zero speed ratio, two underdrive speed ratios, and a direct drive ratio. The front shiftable gearing arrangement can, for example, comprise two simple planetary gear sets and four clutches. Each transmission gearing arrangement also includes a rear shiftable gearing arrangement configured to selectively establish particular speed relationships among the input shaft, the intermediate shaft, and an output shaft. The rear shiftable gearing arrangement can, for example, comprise two simple planetary gear sets and two clutches. Engaging the clutches in various combinations of three establishes nine forward speed ratios and one reverse speed ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a first transmission gearing arrangement;

FIG. 2 is a schematic diagram of a second transmission gearing arrangement;

FIG. 3 is a schematic diagram of a third transmission gearing arrangement;

FIG. 4 is a lever diagram corresponding to the first, second, and third transmission gearing arrangements;

FIG. 5 is a schematic diagram of a fourth transmission gearing arrangement;

FIG. 6 is a schematic diagram of a fifth transmission gearing arrangement;

FIG. 7 is a schematic diagram of a sixth transmission gearing arrangement; and

FIG. 8 is a schematic diagram of a seventh transmission gearing arrangement.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.

A gearing arrangement is a collection of rotating elements and clutches configured to impose specified speed relationships among elements. Some speed relationships, called fixed speed relationships, are imposed regardless of the state of any clutches. A gearing arrangement imposing only fixed relationships is called a fixed gearing arrangement. Other speed relationships are imposed only when particular clutches are fully engaged. A gearing arrangement that selectively imposes speed relationships is called a shiftable gearing arrangement. A discrete ratio transmission has a shiftable gearing arrangement that selectively imposes a variety of speed ratios between an input shaft and an output shaft.

A group of elements are fixedly coupled to one another if they are constrained to rotate at the same speed about the same axis in all operating conditions. Elements can be fixedly coupled by, for example, spline connections, welding, press fitting, or machining from a common solid. Slight variations in rotational displacement between fixedly coupled elements can occur such as displacement due to lash or shaft compliance. In contrast, two elements are selectively coupled by a clutch when the clutch constrains them to rotate at the same speed about the same axis whenever the clutch is fully engaged and they are free to rotate at distinct speeds in at least some other operating condition. Clutches include actively controlled devices such as hydraulically or electrically actuated clutches and passive devices such as one way clutches. A clutch that holds an element against rotation by selectively connecting the element to the housing may be called a brake. A group of elements are coupled if they are fixedly coupled or selectively coupled.

An example transmission is schematically illustrated in FIG. 1. The transmission utilizes four simple planetary gear sets 20, 30, 40, and 50. A simple planetary gear set is a type of fixed gearing arrangement. A planet carrier 22 rotates about a central axis and supports a set of planet gears 24 such that the planet gears rotate with respect to the planet carrier. External gear teeth on the planet gears mesh with external gear teeth on a sun gear 26 and with internal gear teeth on a ring gear 28. The sun gear and ring gear are supported to rotate about the same axis as the carrier. A simple planetary gear set imposes the fixed speed relationship that the speed of the carrier is between the speed of the sun gear and the speed of the ring gear. (This relationship is defined to include the condition in which all three rotate at the same speed.) More specifically, the speed of the carrier is a weighted average of the speed of the sun gear and the speed of the ring gear with weighting factors determined by the number of teeth on each gear. Similar speed relationships are imposed by other known types of fixed gearing arrangements. For example, a double pinion planetary gear set constrains the speed of the ring gear to be a weighted average between the speed of the sun gear and the speed of the carrier.

Carrier 22 is fixedly coupled to carrier 32 and ring gear 28 is fixedly coupled to sun gear 34. This produces a four element fixed gearing arrangement. The first element, sun gear 26, and the fourth element, the combination of ring gear 28 and sun gear 36, always have the most extreme speeds. The speeds of the second element, ring gear 38, and the third element, the combination of carrier 22 and carrier 32, have speeds that are a weighted average of the speeds of the first and fourth elements. Similarly, carrier 42 is fixedly coupled to ring gear 58 and ring gear 48 is fixedly coupled to sun gear 56, producing a second four element fixed gearing arrangement. The fifth element, sun gear 46, and the eighth element, the combination of ring gear 48 and sun gear 56, always have the most extreme speeds. The speeds of the sixth element, the combination of carrier 42 and ring gear 58, and the seventh element, carrier 52, have speeds that are a weighted average of the speeds of the fifth and eighth elements.

A suggested ratio of gear teeth for each planetary gear set in FIG. 1 is listed in Table 1.

TABLE 1 Ring 28/Sun 26 1.85 Ring 38/Sun 36 1.75 Ring 48/Sun 46 1.60 Ring 58/Sun 56 2.30

The sixth element, 42 and 58, is fixedly coupled to output shaft 60. The third element, 22 and 32, is fixedly coupled to the eighth element, 48 and 56, by intermediate shaft 62. Input shaft 64 is selectively coupled to the first element 26 by clutch 66, selectively coupled to the fourth element, 28 and 36, by clutch 68, and selectively coupled to the seventh element 52 by clutch 70. The first element 26 is selectively held against rotation by brake 72, the second element 38 is selectively held against rotation by brake 74, and the fifth element 46 is selectively held against rotation by brake 76.

As shown in Table 2, engaging the clutches and brakes in combinations of three establishes nine forward speed ratios and one reverse speed ratio between input shaft 64 and output shaft 60. An X indicates that the clutch is required to establish the speed ratio. An (X) indicates the clutch can be applied but is not required. When the gear sets of FIG. 1 have tooth numbers as indicated in Table 1, the speed ratios have the values indicated in Table 2. Gear sets 20 and 30, clutches 66 and 68, and brakes 72 and 74 form a front shiftable gearing arrangement that establishes a variety of speed ratios between intermediate shaft 62 and input shaft 64. Specifically, engaging clutch 66 and brake 74 establishes a reverse speed ratio in which intermediate shaft 62 rotates in the opposite direction of input shaft 64. Engaging both brakes 72 and 74 holds intermediate shaft 62 stationary. Engaging clutch 68 in combination with brake 72 and brake 74 respectively establishes two underdrive ratios in which intermediate shaft 62 rotates slower than input shaft 64. Finally, engaging both clutches 66 and 68 establishes a direct drive ratio in which intermediate shaft 62 rotates at the same speed as input shaft 64. Gear sets 40 and 50, clutch 70, and brake 76 form a rear shiftable gearing arrangement that establishes selectable speed relationships among input shaft 64, intermediate shaft 62, and output shaft 60. Specifically, when brake 76 is engaged, an underdrive ratio is established between intermediate shaft 62 and output shaft 60. This underdrive ratio, in combination with various speed ratios established by the front gearing arrangement, establishes the reverse ratio and the first three forward speed ratios of the transmission. When clutch 70 is engaged, the speed of input shaft 64 is constrained to be a weighted average between the speeds of intermediate shaft 62 and output shaft 60. This speed relationship, in combination with various speed ratios established by the front gearing arrangement, establishes the top five forward speed ratios of the transmission. The remaining transmission ratio, 4^(th), is established by engaging clutch 70 and brake 76 together. The front gearing arrangement is not involved in establishing the 4^(th) transmission ratio, but one of the clutches or brakes of the front gearing arrangement can be engaged if desired.

TABLE 2 66 68 70 72 74/78 76 Ratio Step Rev X X X −3.64 81% 1^(st) X X X 4.47 2^(nd) X X X 2.50 1.79 3^(rd) X X X 1.63 1.54 4^(th) (X) X X 1.19 1.37 5^(th) X X X 1.00 1.19 6^(th) X X X 0.87 1.15 7^(th) X X X 0.78 1.11 8^(th) X X X 0.70 1.12 9^(th) X X X 0.61 1.14

Optional one way brake 78 passively holds second element 38 against rotation in one direction while allowing rotation in the other direction. Including this element simplifies the shift from 1^(st) to 2^(nd) gear. If one way brake 78 is present, brake 74 is not engaged in 1^(st) gear. The shift to 2^(nd) gear merely requires the gradual engagement of brake 72. Once the torque capacity of brake 72 is sufficient, one way brake 78 will passively overrun. If one way brake 78 is omitted, then brake 74 is engaged in 1^(st) gear. The shift from 1^(st) gear to 2^(nd) gear is then accomplished by the coordinated release of brake 74 and engagement of brake 72. All remaining shift are accomplished by the coordinated release of one clutch or brake and the engagement of another clutch or brake.

Another example transmission is illustrated in FIG. 2. The transmission utilizes four simple planetary gear sets 80, 90, 100, and 110. Carrier 82 is fixedly coupled to ring gear 98 and ring gear 88 is fixedly coupled to carrier 92, producing a four element fixed gearing arrangement. The first element, sun gear 86, and the fourth element, sun gear 96, always have the most extreme speeds. The speeds of the second element, the combination of carrier 82 and ring gear 98, and the third element, the combination of ring gear 88 and carrier 92, have speeds that are a weighted average of the speeds of the first and fourth elements. Similarly, sun gear 106 is fixedly coupled to sun gear 116 and ring gear 108 is fixedly coupled to carrier 112, producing a second four element fixed gearing arrangement. The fifth element, the combination of sun gear 106 and sun gear 116, and the eighth element, ring gear 118, always have the most extreme speeds. The speeds of the sixth element, the combination of carrier 102 and ring gear 58, and the seventh element, the combination of ring gear 108 and carrier 112, have speeds that are a weighted average of the speeds of the fifth and eighth elements.

A suggested ratio of gear teeth for each planetary gear set in FIG. 2 is listed in Table 3.

TABLE 3 Ring 88/Sun 86 1.85 Ring 98/Sun 96 1.70 Ring 108/Sun 106 3.70 Ring 118/Sun 116 2.30

The sixth element, 102, is fixedly coupled to output shaft 60. The third element, 88 and 92, is fixedly coupled to the eighth element 118 by intermediate shaft 62. Input shaft 64 is selectively coupled to the first element 86 by clutch 66, selectively coupled to the fourth element 96 by clutch 68, and selectively coupled to the seventh element, 108 and 112, by clutch 70. The first element 86 is selectively held against rotation by brake 72, the second element, 82 and 98, is selectively held against rotation by brake 74, and the fifth element, 106 and 116 is selectively held against rotation by brake 76. Optionally, one way brake 78 passively holds second element, 82 and 98, against rotation in one direction while allowing rotation in the other direction.

As shown in Table 4, engaging the clutches and brakes in combinations of three establishes nine forward speed ratios and one reverse speed ratio between input shaft 64 and output shaft 60. When the gear sets of FIG. 2 have tooth numbers as indicated in Table 3, the speed ratios have the values indicated in Table 4.

TABLE 4 66 68 70 72 74/78 76 Ratio Step Rev X X X −3.37 69% 1^(st) X X X 4.92 2^(nd) X X X 2.91 1.69 3^(rd) X X X 1.82 1.60 4^(th) (X) X X 1.27 1.44 5^(th) X X X 1.00 1.27 6^(th) X X X 0.85 1.18 7^(th) X X X 0.76 1.11 8^(th) X X X 0.67 1.14 9^(th) X X X 0.57 1.18

A third example transmission is illustrated in FIG. 3. The transmission utilizes four simple planetary gear sets 120, 130, 140, and 150. Sun gear 126 is fixedly coupled to sun gear 136 by intermediate shaft 135 and ring gear 128 is fixedly coupled to carrier 132, producing a four element fixed gearing arrangement. The first element, the combination of sun gear 126 and sun gear 136, and the fourth element, ring gear 138, always have the most extreme speeds. The speeds of the second element, carrier 122, and the third element, the combination of ring gear 128 and carrier 132, have speeds that are a weighted average of the speeds of the first and fourth elements. Similarly, carrier 142 is fixedly coupled to ring gear 158 and ring gear 148 is fixedly coupled to carrier 152, producing a second four element fixed gearing arrangement. The fifth element, sun gear 146, and the eighth element, sun gear 156, always have the most extreme speeds. The speeds of the sixth element, the combination of carrier 142 and ring gear 158, and the seventh element, the combination of ring gear 148 and carrier 152, have speeds that are a weighted average of the speeds of the fifth and eighth elements.

A suggested ratio of gear teeth for each planetary gear set in FIG. 3 is listed in Table 5.

TABLE 5 Ring 128/Sun 126 2.00 Ring 138/Sun 136 1.90 Ring 148/Sun 146 3.70 Ring 158/Sun 156 1.70

The sixth element, 142 and 158, is fixedly coupled to output shaft 60. The third element, 128 and 132, is fixedly coupled to the eighth element 156 by intermediate shaft 62. Input shaft 64 is selectively coupled to the first element, 126 and 136, by clutch 66, selectively coupled to the fourth element 138 by clutch 68, and selectively coupled to the seventh element, 148 and 152, by clutch 70. The first element, 126 and 136, is selectively held against rotation by brake 72, the second element 122 is selectively held against rotation by brake 74, and the fifth element 146 is selectively held against rotation by brake 76. Optionally, one way brake 78 passively holds second element 122 against rotation in one direction while allowing rotation in the other direction.

As shown in Table 6, engaging the clutches and brakes in combinations of three establishes nine forward speed ratios and one reverse speed ratio between input shaft 64 and output shaft 60. When the gear sets of FIG. 3 have tooth numbers as indicated in Table 5, the speed ratios have the values indicated in Table 6.

TABLE 6 66 68 70 72 74/78 76 Ratio Step Rev X X X −3.46 78% 1^(st) X X X 4.46 2^(nd) X X X 2.64 1.69 3^(rd) X X X 1.73 1.53 4^(th) (X) X X 1.27 1.36 5^(th) X X X 1.00 1.27 6^(th) X X X 0.83 1.20 7^(th) X X X 0.74 1.13 8^(th) X X X 0.63 1.17 9^(th) X X X 0.53 1.19

FIG. 4 describes the transmissions of FIGS. 1, 2, and 3 in the form of a lever diagram. Gear elements which rotate about a common axis and have speeds with a fixed linear relationship are shown along a lever according to their relative speeds. The two elements that have the most extreme speeds are shown at the endpoints of the lever. The remaining elements are shown at intermediate points according to the weighting factors. Lever 160 corresponds to gear sets 20 and 30 of FIG. 1, gear sets 80 and 90 of FIG. 2, and gear sets 120 and 130 of FIG. 3. Any four element fixed gearing arrangement that imposes the designated speed relationships with appropriate weighting factors can be substituted for the corresponding gear sets without impacting the transmission speed ratios. In addition to the fixed gearing arrangements illustrated in FIG. 1-3, many others are known. Any combination of two planetary gear sets with two elements of each fixedly connected to two elements of the other forms a four element fixed gearing arrangement. Some fixed gearing arrangements will be preferable to others in terms of packaging, efficiency, and planet gear speeds. Similarly, lever 162 corresponds to gear sets 40 and 50 of FIG. 1, gear sets 100 and 110 of FIG. 2, and gear sets 140 and 150 of FIG. 3. Any four element fixed gearing arrangement that imposes the designated speed relationships can be substituted for the corresponding gear sets.

A fourth example transmission is illustrated in FIG. 5. The transmission utilizes four simple planetary gear sets 210, 220, 230, and 240. Ring gear 218 and carrier 222 are fixedly coupled to sun gear 246 by intermediate shaft 62. Carrier 232 is fixedly coupled to output shaft 60. Sun gear 226 and carrier 242 are fixedly coupled to input shaft 64. Sun gear 236 is fixedly held against rotation. A suggested ratio of gear teeth for each planetary gear set in FIG. 5 is listed in Table 7.

TABLE 7 Ring 218/Sun 216 1.85 Ring 228/Sun 226 1.70 Ring 238/Sun 236 1.60 Ring 248/Sun 246 2.30

Sun gear 216 is selectively coupled to input shaft 64 by clutch 250 and selectively held against rotation by brake 256. Carrier 212 is selectively coupled to ring gear 228 by clutch 252 and selectively held against rotation by brake 258. Ring gear 238 is selectively coupled to sun gear 246 and intermediate shaft 62 by clutch 260. Ring gear 248 is selectively coupled to carrier 232 and output shaft 60 by clutch 254. Optionally, one way brake 262 passively holds carrier 212 against rotation in one direction while allowing rotation in the other direction.

As shown in Table 8, engaging the clutches and brakes in combinations of three establishes nine forward speed ratios and one reverse speed ratio between input shaft 64 and output shaft 60. When the gear sets of FIG. 5 have tooth numbers as indicated in Table 7, the speed ratios have the values indicated in Table 8.

TABLE 8 250 252 254 256 258/262 260 Ratio Step Rev X X X −3.01 69% 1^(st) X X X 4.39 2^(nd) X X X 2.59 1.69 3^(rd) X X X 1.63 1.60 4^(th) (X) X X 1.19 1.37 5^(th) X X X 1.00 1.19 6^(th) X X X 0.86 1.16 7^(th) X X X 0.79 1.10 8^(th) X X X 0.70 1.13 9^(th) X X X 0.60 1.16

A fifth example transmission is illustrated in FIG. 6. The transmission utilizes four simple planetary gear sets 310, 320, 330, and 340. Ring gear 318 is fixedly coupled to ring gear 338 and sun gear 346 by intermediate shaft 62. Carrier 312 is fixedly coupled to ring gear 328. Sun gear 326 and carrier 342 are fixedly coupled to input shaft 64. Sun gear 336 is fixedly held against rotation. A suggested ratio of gear teeth for each planetary gear set in FIG. 5 is listed in Table 9.

TABLE 9 Ring 318/Sun 316 1.85 Ring 328/Sun 326 1.70 Ring 338/Sun 336 1.60 Ring 348/Sun 346 2.30

Sun gear 316 is selectively coupled to input shaft 64 by clutch 350 and selectively held against rotation by brake 356. Carrier 312 and ring gear 328 are selectively held against rotation by brake 358. Carrier 322 is selectively coupled to ring gear 318 and intermediate shaft 62 by clutch 352. Output shaft 60 is selectively coupled to carrier 332 by clutch 360 and selectively coupled to ring gear 348 by clutch 354. Optionally, one way brake 362 passively holds carrier 312 and ring gear 328 against rotation in one direction while allowing rotation in the other direction.

As shown in Table 10, engaging the clutches and brakes in combinations of three establishes nine forward speed ratios and one reverse speed ratio between input shaft 64 and output shaft 60. When the gear sets of FIG. 6 have tooth numbers as indicated in Table 9, the speed ratios have the values indicated in Table 10.

TABLE 10 350 352 354 356 358/362 360 Ratio Step Rev X X X −3.01 69% 1^(st) X X X 4.39 2^(nd) X X X 2.59 1.69 3^(rd) X X X 1.63 1.60 4^(th) (X) X X 1.19 1.37 5^(th) X X X 1.00 1.19 6^(th) X X X 0.86 1.16 7^(th) X X X 0.79 1.10 8^(th) X X X 0.70 1.13 9^(th) X X X 0.60 1.16

A sixth example transmission is illustrated in FIG. 7. The transmission utilizes four simple planetary gear sets 410, 420, 430, and 440. Ring gear 418 is fixedly coupled to ring gear 438 and sun gear 446 by intermediate shaft 62. Sun gear 426 is fixedly coupled to intermediate shaft 415. Ring gear 428 and carrier 442 are fixedly coupled to input shaft 64. Carrier 412 and sun gear 436 are fixedly held against rotation. A suggested ratio of gear teeth for each planetary gear set in FIG. 7 is listed in Table 11.

TABLE 11 Ring 418/Sun 416 2.00 Ring 428/Sun 426 1.90 Ring 438/Sun 436 1.60 Ring 448/Sun 446 2.30

Intermediate shaft 415 is selectively coupled to input shaft 64 by clutch 450, selectively coupled to sun gear 416 by clutch 458, and selectively held against rotation by brake 456. Carrier 422 is selectively coupled to ring gear 418 and intermediate shaft 62 by clutch 452. Output shaft 60 is selectively coupled to carrier 432 by clutch 460 and selectively coupled to ring gear 448 by clutch 454.

As shown in Table 12, engaging the clutches and brakes in combinations of three establishes nine forward speed ratios and one reverse speed ratio between input shaft 64 and output shaft 60. When the gear sets of FIG. 7 have tooth numbers as indicated in Table 11, the speed ratios have the values indicated in Table 12.

TABLE 12 450 452 454 456 458 460 Ratio Step Rev X X X −3.25 78% 1^(st) X X X 4.19 2^(nd) X X X 2.48 1.69 3^(rd) X X X 1.63 1.53 4^(th) (X) X X 1.19 1.37 5^(th) X X X 1.00 1.19 6^(th) X X X 0.87 1.15 7^(th) X X X 0.79 1.10 8^(th) X X X 0.70 1.13 9^(th) X X X 0.61 1.15

A seventh example transmission is illustrated in FIG. 8. The transmission utilizes four simple planetary gear sets 510, 520, 530, and 540. Carrier 522 is fixedly coupled to ring gear 538 by intermediate shaft 62. Sun gear 516 is fixedly coupled to intermediate shaft 515. Ring gear 548 is fixedly coupled to output shaft 60. Ring gear 528 and carrier 542 are fixedly coupled to input shaft 64. Carrier 512 and sun gear 536 are fixedly held against rotation. A suggested ratio of gear teeth for each planetary gear set in FIG. 8 is listed in Table 13.

TABLE 13 Ring 518/Sun 516 2.00 Ring 528/Sun 526 1.90 Ring 538/Sun 536 1.60 Ring 548/Sun 546 2.30

Intermediate shaft 515 is selectively coupled to input shaft 64 by clutch 550, selectively coupled to sun gear 526 by clutch 552, and selectively held against rotation by brake 556. Ring gear 518 is selectively coupled to carrier 522 and intermediate shaft 62 by clutch 558. Output shaft 60 is selectively coupled to carrier 532 by clutch 560. Sun gear 546 is selectively coupled to intermediate shaft 62 by clutch 554.

As shown in Table 14, engaging the clutches and brakes in combinations of three establishes nine forward speed ratios and one reverse speed ratio between input shaft 64 and output shaft 60. When the gear sets of FIG. 8 have tooth numbers as indicated in Table 13, the speed ratios have the values indicated in Table 14.

TABLE 14 550 552 554 556 558 560 Ratio Step Rev X X X −3.25 78% 1^(st) X X X 4.19 2^(nd) X X X 2.48 1.69 3^(rd) X X X 1.63 1.53 4^(th) (X) X X 1.19 1.37 5^(th) X X X 1.00 1.19 6^(th) X X X 0.87 1.15 7^(th) X X X 0.79 1.10 8^(th) X X X 0.70 1.13 9^(th) X X X 0.61 1.15

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications. 

What is claimed is:
 1. A transmission comprising: an input shaft; an output shaft; first and second intermediate shafts; a first shiftable gearing arrangement comprising a simple planetary gear set having a sun gear, a planet carrier fixedly held against rotation, a ring gear fixedly coupled to the first intermediate shaft, and a plurality of planet gears supported for rotation relative to the planet carrier and in continuous meshing engagement with both the sun gear and the ring gear, wherein the first shiftable gearing arrangement is configured to selectively constrain the first intermediate shaft and the second intermediate shaft to rotate in opposite directions or to both be stationary; a second shiftable gearing arrangement configured to selectively constrain the first intermediate shaft to rotate at a first intermediate shaft speed between speeds of the second intermediate shaft and of the input shaft; a third shiftable gearing arrangement configured to selectively constrain the output shaft to rotate at an output shaft speed between zero and the first intermediate shaft speed and to selectively constrain the input shaft to rotate at an input shaft speed between the first intermediate shaft speed and the output shaft speed; a first clutch selectively coupling the second intermediate shaft to the input shaft; and a first brake selectively holding the second intermediate against rotation; and a second clutch selectively coupling the sun gear to the second intermediate shaft.
 2. The transmission of claim 1 wherein the second shiftable gearing arrangement comprises a simple planetary gear set having a sun gear fixedly coupled to the second intermediate shaft, a planet carrier, a ring gear fixedly coupled to the input shaft, and a plurality of planet gears supported for rotation relative to the planet carrier and in continuous meshing engagement with both the sun gear and the ring gear; and a third clutch selectively coupling the planet carrier to the first intermediate shaft.
 3. The transmission of claim 1 wherein the third shiftable gearing arrangement comprises a fourth shiftable gearing arrangement configured to selectively constrain the output shaft speed to be between zero and the first intermediate shaft speed; and a fifth shiftable gearing arrangement configured to selectively constrain the input shaft speed to be between the first intermediate shaft speed and the output shaft speed.
 4. The transmission of claim 3 wherein the fourth shiftable gearing arrangement comprises a simple planetary gear set having a sun gear fixedly held against rotation, a planet carrier, a ring gear fixedly coupled to the first intermediate shaft, and a plurality of planet gears supported for rotation relative to the planet carrier and in continuous meshing engagement with both the sun gear and the ring gear; and a fifth clutch selectively coupling the planet carrier to the output shaft.
 5. The transmission of claim 3 wherein the fifth shiftable gearing arrangement comprises a simple planetary gear set having a sun gear fixedly coupled to the first intermediate shaft, a planet carrier fixedly coupled to the input shaft, a ring gear, and a plurality of planet gears supported for rotation relative to the planet carrier and in continuous meshing engagement with both the sun gear and the ring gear; and a sixth clutch selectively coupling the ring gear to the output shaft.
 6. A transmission comprising: an input; a transmission case; and four planetary gearsets having first through fourth suns, carriers, and rings respectively wherein the first carrier and the third sun are fixedly coupled to the transmission case, the second ring and the fourth carrier are fixedly coupled to the input, and the first ring, the third ring, and the fourth sun are mutually fixedly coupled to one another and selectively coupled to the second carrier.
 7. The transmission of claim 6 further comprising an output selectively coupled to the third carrier and selectively coupled to the fourth ring.
 8. The transmission of claim 7 wherein the second sun is selectively coupled to the first sun, selectively coupled to the input, and selectively coupled to the transmission case.
 9. A transmission comprising: an input; a transmission case; and four planetary gearsets having first through fourth suns, carriers, and rings respectively wherein the first carrier and the third sun are fixedly coupled to the transmission case, the second ring and the fourth carrier are fixedly coupled to the input, and the third ring is coupled to the first ring, the second carrier, and the fourth sun.
 10. The transmission of claim 9 wherein the third ring is fixedly coupled to the first ring and the fourth sun and selectively coupled to the second carrier.
 11. The transmission of claim 9 wherein the third ring is fixedly coupled to the second carrier, selectively coupled to the first ring, and selectively coupled to the fourth sun. 